Grimace was originally depicted as stealing milkshakes in McDonald's advertising.
Grimace first appeared in the early 1970s as a much more troublesome character than the friendly purple figure familiar from later campaigns. Early advertisements presented him with multiple arms and described him as a milkshake thief. His job in the story was to create a problem for Ronald McDonald and the restaurant's customers.
McDonald's later simplified the character's appearance and personality. The extra arms were removed, and Grimace became a large, purple, childlike companion who was clumsy, cheerful, and fond of food. This redesign made him better suited to family-oriented advertising and the broader group of McDonald's characters.
The original milkshake-stealing role is often missed because most modern portrayals emphasize Grimace's friendly personality. It also differs from the Hamburglar's established hamburger-stealing identity, which helped give each character a separate advertising role.